Help Needed For First Semi-Aiuto Project

[Air2theBrain]

Hi everyone, whilst i have been putting together a qev for a semi-auto project, i realized i had an old Sceptor markerball paintball gun dis-assembled, and wanted to ask if it would be ok for a first semi-auto?

The best thing about it is that it has a semi-auto firing mechanism.

The tank needs around 30-40 pumps to fill, then with every trigger press it releases a small amount of air until the tank needs to be re-filled again. It isn't really a paintball gun, more a toy blaster, but quite powerful in its standard form.

I want it to shoot 6mm ammo, and i will have a breech barrel and ammo feed for semi-auto.

Originally i was going to have the qev, etc inside the frame but looking at it more and more i thought why not keep its semi-auto function and just reinforce everything and bypass the tank and attach a barrel, etc?

I also thought the tank that is made to look like a paint ball ammo mag could be made to hold the ammo?



Would greatly appreciate any help, will post pics of my qev set up soon.

Thanks everyone, cant wait to get this up and running.

[jackssmirkingrevenge]

If you want to go to a smaller caliber, I don't think there's anything you can reuse except the external shell in this case.

[Air2theBrain]

Hi Jack and thanks for your reply.

The blaster originally fired 2.4g soft balls and really launched them hard despite all the dead space and a very restrictive barrel.

It's a good quality construction, metal sear and just a nifty semi-auto trigger system on it which i thought would have to be taken advantage of.

I'm tempted to make a custom frame for the qev, but currently waiting on a better trigger, for the air gun i have now simply doesn't force enough air through the qev. I ordered a slide-valve then realized that's not going to suit, so i found a proper trigger system which will work much better.


Forgive the qev picture, originally i was wanting to go full-auto but i only really want semi-auto at the moment. But that set-up pictured never worked when attached to my air compressor...the qev just farted a little, with no pop-off sound or anything.

I will have to put a gauge on this blasters tank to see how much pressure is being used for every shot.

I found a couple of fire extinguishers which was great, and a very old and large steel gas tank, not sure if i could use it..but if i could then that would hold a lot of air.

Please forgive the pictures, i will use a proper photo uploader next time

I purchased a new compressor, my old one kicked the bucket not long ago, but this one is much better, 2.5HP, 140liters per minute, so will be good to fill tanks with, currently looking for a scuba tank at the moment.


This is my first attempt at a qev set-up, as i mentioned when applying air nothing happened...not sure if the chamber is big enough or if it should have been capped off, but i had a pop-off valve installed so maybe that needed to be modified i'm not sure.
I will find out soon, the slide valve should arrive today, can get rid of the air gun then and use that until the trigger arrives.

[farcticox1]

Nice compressor, what's the max PSI

[Air2theBrain]

Thanks farcticox1, only 180psi

[farcticox1]

Nice, that would suit me fine.

[Air2theBrain]

it should be good, not very good for filling scuba tanks i've heard..but time will tell.

I'm going to mod the large fire extinguisher i have so i can just connect the compressor onto it and fill her up, but the large gas tank i have will be great to fill, just need to get it looked at first i think.
The large tank was sitting on my friends country property for years until i rescued it, that and the extinguisher also..love freebies

[Air2theBrain]

Did a quick mock up when the slide valve arrived today.


I thought the smaller extinguisher would be great for the air/firing chamber, just need to find the right attachments for it.

Shame i can't use my old airsoft barrel from my old BASR, 6mm bearings are a little too big for it, but for a mock up it helps to get a general picture.

I really need to start on my barrels also, but would rather have all the attachments ready to go..really need to find a main supply tank.

[jackssmirkingrevenge]

Looks good, one thing to consider though is that your firing chamber is far, far too big for an airsoft barrel, the one you have here is more than adequate for a very good performance at 100 psi+.

originally i was wanting to go full-auto but i only really want semi-auto at the moment. But that set-up pictured never worked when attached to my air compressor...the qev just farted a little, with no pop-off sound or anything.

This is likely because you were filling from the pilot side, so the pilot dump was competing with the air supply.

Here's what I did for full auto with a QEV:

[youtube][/youtube]

You don't necessarily need to machine a new piston, just make a small hole in the edge of the existing piston so air can flow from the chamber to the pilot area.

[Air2theBrain]

Ooh lovely will have the drill ready when going to mod the qev for full-auto, thanks very much Jack.

Oh the barrel from my old airsoft sniper rifle(BASR) was just for mock up.

Will have a barrel much longer for sure. That barrel has been sitting here for years, my airsoft rifle now has a 430mm barrel in it, 600fps with a 2.0g bb, i cranked the hop-up once to an un-realistic hop and maxed it out at 620fps with a 170 spring.

Oh i was filling from the P side!

Does that mean i can cap off P....and fill from A?

[jackssmirkingrevenge]

Does that mean i can cap off P....and fill from A?

With a slide check or similar three way valve you can fill from P, because the action of the valve empties the pilot while simultaneously cutting off the air supply from the main chamber.

Will have a barrel much longer for sure. That barrel has been sitting here for years, my airsoft rifle now has a 430mm barrel in it, 600fps with a 2.0g bb, i cranked the hop-up once to an realistic hop and maxed it out at 620fps with a 170 spring.

0.20g BB I guess?

Here's a little simulation I did for a 0.45g airsoft BB with a 24 inch barrel firing at 150 psi:



You can see from the data that increasing the volume of the chamber is a game of diminishing returns in terms of performance gain. Your fire extinguisher looks to be about 10 ci which as you can see is far too big, you can halve the volume and lose only 5% of projectile energy at the muzzle.

[Air2theBrain]

Yep was with a 0.2g bb for sure. Has the TDC mod for the hop.

Wow thats mighty fine FPS ratings with a 0.45g bb holy hell!

[Air2theBrain]

Love the variations in chamber volumes, thanks so much for that!

Yeah agreed the chamber is huge, i will keep that one for a bigger project.

[Air2theBrain]

Slide valve worked a treat, gave it a quick test so happy with what i have at the moment.


Hope to have a barrel done by tomorrow then i can start testing on the weekend.

For the toy blaster i'm going to give it a new air line with a t-piece so i can put a gauge on to see how much psi the standard tank needs to be filled.

I thought i could keep the standard tank and have that tank fed by another chamber always keeping it full?

Main focus is the qev right now, hopefully the trigger arrives tomorrow to replace the slide valve, then its just a matter of barrel and semi-auto feed.

[jackssmirkingrevenge]

Slide valve worked a treat, gave it a quick test so happy with what i have at the moment.

Nice if I could make one suggestion, don't connect the gauge to the pilot side. This adds volume, and for the best performance and efficiency the pilot area should be as small as possible.